Various stereoscopic image display devices for obtaining a stereoscopic image from a flat display has been proposed. For such a stereoscopic image display device which displays a stereoscopic image, the following three systems are widely adopted other than the hologram system.
According to the first system, a single image display device alternatively displays a right eye-use image and a left eye-use image in a time sharing manner. This system is arranged so that a stereoscopic image can be obtained based on the fact that an observer wears shutter spectacles whose right and left lenses open and close alternatively in synchronism with the alternating of the images.
According to the second system, a right eye-use image and a left eye-use image are alternatively displayed in a stripe manner by a single image display device. Then, a lenticular lens or slits, provided in a vicinity of the display device, assigns the displayed image to the right and left eyes respectively.
The third system is referred to as a polarizing spectacles system. This system is arranged so that planes of polarization of outgoing light from a right eye-use pixel and a left eye-use pixel are orthogonal, and image information of the right eye-use pixel and the left eye-use pixel are directed to the right and left eyes by polarizing plates provided to the spectacles worn by the observer to be perceived by the respective eyes. Note that, in this system, clockwise and anti-clockwise circularly polarized light may be used instead of the orthogonal planes of polarization.
The described three systems are based on a principle in which depth perception is organized by separately displaying parallax of right eye-use image and left eye-use image so as to be perceived by the respective eyes of the observer.
The following will describe respective characteristics of the three stereoscopic image systems.
According to the first system, a stereoscopic image displaying can be carried out by a single display device, thereby ensuring that the resolution of the display device can be prevented from lowering, and a stereoscopic image display region is not limited. Nevertheless, because the spectacles to be worn by the observer are heavy due to the shutter function, it is not suitable for use in a long period of time. Further, the spectacles with such function are expensive.
According to the second system, a stereoscopic image can be observed without wearing spectacles. However, the second system has a drawback in that the observer is required to fix his or her head since the stereoscopic image display region is limited.
According to the third system, it is required for the observer to wear spectacles with a specific function, yet the spectacles required in the third system are not as expensive and complex as that used in the first system, i.e., the spectacles of the third system are lighter and inexpensive. Further, a stereoscopic image can be observed by a plurality of observers with the respective spectacles, thereby having an advantage over the second system in that the stereoscopic image display region is not limited.
However, in the third system, in order to display images having different polarization directions, a system for combining images produced by two display devices or two projectors with a half mirror or a polarizing mirror is widely adopted. Consequently, the third system has a drawback in that the cost of the display device becomes high due to an increase in the number of constituting components, and therefore the third system is not suitable for home-use.
As a countermeasure, a polarizing plate (micro polarizing plate) composed of two types of polarizing plates which are arranged in a mosaic or a stripe manner on a single plane and their polarizing axes are orthogonal to each other has been invented. The polarizing plate of this type permits a single display device to display both the right eye-use image and the left eye-use image.
For example, Japanese Unexamined Patent publication No. 184929/1983 (Tokukaisho 58-184929) discloses a micro polarizing plate composed of two types of plane polarizing plates which are arranged in a mosaic manner so that the polarizing axes are orthogonal to each other. According to the above publication, the micro polarizing plate is provided in front of the display device, and an image is allowed to pass through spectacles having a pair of polarizing plates whose polarizing axes are orthogonal to each other. As a result, the right eye-use image and the left eye-use image are separated by the polarizing plates to be perceived by the respective eyes of the observer, thereby realizing a stereoscopic image.
Here, as the display device, a CRT (Cathode Ray Tube) or a liquid crystal panel (Liquid Crystal Display), etc. is adopted. In the case of adopting the CRT, the micro polarizing plate is provided in front of a display tube. In contrast, in the case of adopting the liquid crystal panel, since polarizing plates are already provided on the both sides of the liquid crystal panel, the polarizing plate on the side of the observer, or the polarizing plates on the side of the observer as well as on the side of a backlight are replaced with the micro polarizing plates.
FIG. 10 illustrates an arrangement of a stereoscopic image display device in which a liquid crystal panel is adopted as a display device, and two types of polarizing plates are arranged in a stripe manner in a horizontal row on both surfaces of the liquid crystal panel such that the polarizing axes of the two types of polarizing plates are orthogonal to each other for each row.
A stripe pitch of the two types of polarizing plates in a vertical column direction is substantially equal to a pixel pitch of a liquid crystal panel 51 in the vertical column direction. A left eye-use image information display region 52 and a right eye-use image information display region 53 are formed alternatively in the vertical column direction. With this arrangement, when viewed with polarizing spectacles 54, image information of the left eye-use image information display region 52 and the right eye-use image information display region 53 are separated by the polarizing spectacles 54 to be perceived by the respective eyes of the observer, thereby creating a stereoscopic image from the displayed image.
A method for manufacturing the micro polarizing plate, for example, is disclosed in U.S. Pat. No. 5,327,285 in detail. The following will describe the method for manufacturing the micro polarizing plate disclosed in the above U.S. Patent referring to FIG. 11(a) through FIG. 11(d).
Firstly, as shown in FIG. 11(a), a polarizing plate 62 is attached to a glass substrate 61. As the material of the polarizing plate 62, uniaxially extended PVA (polyvinyl alcohol) dyed with iodine is widely adopted; nonetheless, other materials may be substituted therefor. Secondly, as shown in FIG. 11(b), a photoresist 63 is applied in such a manner that the photoresist 63 is patterned on every other row, e.g., in a stripe manner, in the same interval as the pixel pitch. Here, for example, P.sub.1 in FIG. 11(b) indicates the width of a pixel of the right eye-use image information, and P.sub.2 in FIG. 11(b) indicates the width of a pixel of the left eye-use image information.
Thirdly, as shown in FIG. 11(c), the polarizing plate 62 is decolorized with potassium hydroxide (KOH) etc. by using the photoresist 63 as a mask to form a non-polarizing region 64. Instead, the polarizing region may be formed by (1) using an undyed substrate as the polarizing plate 62, next (2) the polarizing plate 62 is dyed with iodine through holes formed by patterning, then (3) the polarizing plate 62 is stabilized by boric acid.
Finally, the photoresist 63 is removed, and another substrate having the same arrangement is prepared. Then, as shown in FIG. 11(d), the two substrates thus prepared are positioned and combined together such that the directions of the polarizing axes of the polarizing plates 62 provided to each substrate are orthogonal to each other, thereby obtaining the micro polarizing plate.
Note that, beside decolarizing or dying the polarizing plate 62, a method for directly etching the polarizing plate 62 may be employed as well. In the case where the PVA is used as the polarizing plate 62, the polarizing plate 62 can be etched directly with water and ethanol. Further, in the case where resin other than PVA is used as the polarizing plate 62, the polarizing plate 62 can be etched directly by reactive ion etching and laser etching. The following will describe the steps for forming the micro polarizing plate by etching.
As shown in FIG. 12(a) and FIG. 12(b), the polarizing plate 62 is attached to the substrate 61, and the photoresist 63 is applied to the polarizing plate 62 for patterning, these steps being the same as those in the above-described method. Next, instead of decolorizing or dying the polarizing plate 62, as shown in FIG. 12(c), the polarizing plate 62, for example, is etched with water and ethanol by using the photoresist 63 as a mask. Then, the photoresist 63 is removed, and another substrate having the same arrangement is prepared. Then, as shown in FIG. 12(d), the two substrates thus prepared are positioned and combined together such that the directions of the polarizing axes of the polarizing plates 62 attached to each substrate are orthogonal to each other, thereby obtaining the micro polarizing plate.
Here, in FIG. 11(d) and FIG. 12(d), the micro polarizing plate is formed by combining the glass side of one substrate and the polarizing layer side of the other polarizing plate. Instead, for example, the micro polarizing plate may be formed by combining the substrates so that the surfaces on which each polarizing plate 62 is formed to face with each other, or so that the glass substrates 61 neighbor with each other.
Here, in the case of the stripe polarizing plate, the micro polarizing plate may be formed by directly dividing up the polarizing plate in a stripe manner, and thereafter combining two types of substrates with each other.
Further, instead of forming the polarizing plate 62 on the substrate 61, it may be possible that (1) a quarter wavelength plate is formed on the substrate (not shown), (2) a mosaic or a stripe retardation plate is prepared by the same method as above, and (3) the mosaic or stripe retardation plate thus prepared is positioned outside a polarizing plate, which has not been patterned, so that circularly polarized light rotating in the opposite direction are projected. In this case, a stereoscopic image can be obtained by observing with spectacles having circular polarizing plates.
The afore-mentioned U.S. Patent, as shown in FIG. 13, discloses an arrangement wherein a half wavelength plate 71 is provided on the side of an image display of either right eye-use or left eye-use. With this arrangement, the half wavelength plate 71 rotates the polarization direction of the light that has been transmitted through the polarizing plate 72 by 90.degree.. Therefore, when viewed with polarizing spectacles (not shown), a stereoscopic image can be obtained.
Furthermore, the afore-mentioned U.S. Patent also discloses an arrangement wherein TN (Twisted Nematic) liquid crystal cell is provided outside the display device. Specifically, as shown in FIG. 14, TN liquid crystal 82 is sandwitched between two glass substrates 81, and a TN liquid crystal cell 84 having the same pixel pitch as that of a display device 83 is provided in front of the display screen of the display device 83. Here, the TN liquid crystal 82 is aligned in a twisted manner by 90.degree..
According to the above arrangement, the light that has been transmitted through the display device 83 enter the TN liquid crystal cell 84 through a polarizing plate 85. Here, for example, if a voltage is applied only to the region B of FIG. 14, the light passing through the region B leaves the TN liquid crystal cell 84 without optical rotation. On the other hand, the light passing through the region A leaves the TN liquid crystal cell 84 after being subjected to the optical rotation by 90.degree. according to the alignment of the TN liquid crystal 82.
With the described arrangement, by providing the TN liquid crystal cell 84 so as to be in front of the display screen, the light from each pixel is subjected to optical rotation so as to correspond to image information of right eye-use or left eye-use. Namely, the TN liquid crystal cell 84 has the same function as the above-mentioned half wavelength plate 71 (see FIG. 13).
However, according to the method for manufacturing the micro polarizing plate disclosed in the above U.S. Patent, since the micro polarizing plate is prepared by combining the two different substrates so that the directions of the polarizing axes are orthogonal to each other, it is required to position the substrates with precision during combining thereof. FIG. 15(a) illustrates a case where the polarizing layer of one substrate and the glass side of the other substrate are not appropriately combined, causing a positioning error. FIG. 15(b) illustrates a case where the respective polarizing layers of the two substrates are not appropriately combined, causing a positioning error.
As indicated by the regions D in FIG. 15(a) and FIG. 15 (b), in the case where the polarizing plates 62 are overlapped with each other due to inappropriate combining of the substrates, no light is allowed to transmit through the overlapped region since the polarizing axes of the polarizing plates 62 are orthogonal to each other in the overlapped region. Therefore, in the case of the stripe polarizing plate, a black line is generated in the same direction as the direction of the stripe.
On the other hand, as indicated by the regions C in FIG. 15(a) and FIG. 15(b), when a gap is created between the polarizing plates 62 due to a positioning error during combining of the substrates, the light passes through the gap. As a result, a white line (blank) is generated regardless of information to be displayed.
In short, the described arrangement has a drawback in that a black line and a blank etc. are generated in the case where a positioning error is generated due to the lowering of the accuracy of the combining of the substrates, thereby lowering the visibility.
Further, even in the case where the polarizing layer of one substrate and the glass side of the other substrate are combined with precision, since the glass substrate 61 exists between the two polarizing plates 62, if observed from certain directions, a black line and a blank etc. are still generated, thereby lowering the visibility as well.
Specifically, as shown in FIG. 16, since outgoing light 91 from the liquid crystal panel 51 perpendicular to the glass substrate 61 passes through the polarizing plates 62 corresponding to each pixel, no problem arises. On the other hand, light 92, for example, diagonally emitted from the liquid crystal panel 51 to the glass substrate 61 passes through two polarizing plates 62 whose polarizing axes are orthogonal to each other, such that the display in this direction always appears black. In contrast, light 93, for example, diagonally emitted from the liquid crystal panel 51 to the glass substrate 61 in the same manner as the light 92 passes through no polarizing plate 62, such that the display in this direction always appears white regardless of information to be displayed.
As described, the above arrangement has a drawback in that even if the two substrates are combined with precision, if observed from certain directions, there create (1) a region in which image information of the right eye-use and left eye-use is not displayed and (2) a region in which no image is displayed, thereby lowering the visibility.
Further, as shown in FIG. 13, in the case where the half wavelength plates 71 are attached in a slit manner, it becomes difficult to provide the half wavelength plates 71 in a stripe manner with precision. Namely, in cutting processing, it is difficult to cut the half wavelength plates 71 in a stripe manner so as to precisely correspond to the pixel pitch, and a long time is required for the processing. In contrast, in etching processing, the above-mentioned polarizing plate 62 (see to FIG. 11) can be etched in an order of tens of .mu.m; however, in the half wavelength plate 71, the amount of etching is in an order of 100 .mu.m to 200 .mu.m, thereby making it difficult to carry out etching with high pitch accuracy in the direction of its thickness.
Furthermore, as shown in FIG. 14, in the arrangement where the TN liquid crystal cell 84 is provided in front of the display screen of the display device 83, transmitted light is selectively subjected to optical rotation by applying a voltage to pixels of right eye-use or left eye-use, thereby requiring an electric circuit for driving the TN liquid crystal cell 84; consequently, the device becomes thick and heavy, and the cost becomes high.